Therefore also now, saith the Lord, turn ye even to me with all your heart, and with fasting, and with weeping, and with mourning. (Joel 2:12)
The word "turn" means "repent." God says to His people whose hearts are turned from Him, "Repent." Repent means primarily to change your mind. You indicate a change of mind by turning around. The by-product of repentance will be fasting, weeping, and mourning. Unfortunately, a great many people think that if they go down to an altar and shed enough tears, they are converted. Well, I went through that process as a boy and found it to be absolutely meaningless.
And rend your heart, and not your garments, and turn unto the Lord your God: for he is gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil. (Joel 2:13)
You see, this was to be a heart experience, not some outward gesture. Actually, the Mosaic Law forbade the priest from tearing his garments. Repentance was not to be shown by being a fanatic. The tear was to be in the heart.
Now he gives the reason for turning to the Lord: "For he is gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil." In the Books of Exodus and Jonah, I deal more thoroughly with the question of what it means when God repents. When Israel was in Egypt, it looked as if God changed His mind. He sent plague after plague to Egypt to give Pharaoh the opportunity to repent and turn to Him, but he didn't. Also in Jonah's day, God sent Jonah to preach to the Ninevites that He would destroy the city. However, Ninevah repented and turned to God; so God did not destroy the city. It looked as if God had changed His mind after He said that He would destroy the city, but He did not change His mind. God is immutable. He is always gracious; He is always merciful, and He is always slow to anger.
My friend, you can always depend upon God. He never changes, He is immutable; but when a sinner repents and turns to Him, God says in effect, "You were under My judgment, and I was going to judge you, but now that you have turned to Me, I will not judge you." God is always gracious and ready to forgive.
My friend, the only way we can come to Him is to come as sinners wanting to turn from our sins. If you have been turning from God and now will turn to God, all you have to do is call upon Him and He will save you. "...Believe on the Lord Jesus Christ, and thou shalt be saved..." (Acts 16:31). You don't need to do anything but that. You don't need to join a church, go through a ceremony, or promise Him something. You simply turn as a sinner to Christ for His mercy.
—From Edited Messages on Joel by Dr. J. Vernon McGee